The National Convective Weather Forecast
(NCWF) product, designed and implemented by the National Center for
Atmospheric Research (NCAR), provides current convective hazards and
1-hour extrapolation forecasts of thunderstorm hazard locations. The
hazard field and forecasts update every 5 minutes.

The diagnostic analysis combines WSR-88D
national radar and echo top mosaics (provided by NOAA with mosaics
created and distributed by UNISYS) and cloud-to-ground lightning
(provided by Global Atmospherics Inc). The Convective Hazard Detection
field is depicted based on a 6 level intensity scale. The 6 levels
fundamentally correspond to VIP level.

Forecasts are determined by applying a
stratiform-convective partitioner (Steiner et.al. 1985) and an
elliptical filter (Wolfson et al. 1998) to the hazard detection field.
These filters eliminate stratiform return and small-scale perishable
features that are not a hazard to aviation or are not likely to
persist for 1 hour, respectively. Extrapolations are performed based
on the Thunderstorm Identification Tracking and Nowcasting (TITAN,
Dixon and Wiener 1993) algorithm.

The NCWF forecast product does well with
long-lived mature systems. However, the initiation, growth, and
dissipation of these systems, as well as shorter-lived isolated
storms, are not well forecast. Work on automated methods to forecast
the growth and dissipation of storms is on going.

Description

The NCWF is an automatically generated depiction of: (1) current
convection and (2) extrapolated significant current convection. It is
a supplement to, but does NOT substitute for, the report and forecast
information contained in Convective SIGMETs (see paragraph 7-1-5c).
Convection, particularly significant convection, is typically
associated with thunderstorm activity.

The National Weather Service Aviation Weather Center (AWC) updates
the NCWF based on input from the Next Generation Weather Radar
(NEXRAD) and cloud-to-ground lightning data.

The NCWF is most accurate for long-lived mature multi-storm
systems such as organized line storms. NCWF does not forecast
initiation, growth or decay of thunderstorms. Therefore, NCWF tends to
under-warn on new and growing storms and over-warn on dying storms.
Forecast positions of small, isolated or weaker thunderstorms are not
displayed.

Attributes

The NCWF is updated frequently (every 5 minutes) using the most
current available data.

The NCWF is able to detect the existence of convective storm
locations that agree very well with concurrent radar and lightning
observations.

The NCWF is a high-resolution forecast impacting a relatively
small volume of airspace rather than covering large boxed areas. The
location, speeds and directions of movement of multiple convective
storms are depicted individually.

The NCWF extrapolation forecasts are more accurate when predicting
the location and size of well organized, unchanging convective storms
moving at uniform speeds. The NCWF does not work well with sporadic,
explosive cells developing and dissipating in minutes.

The NCWF may not detect or forecast:

Some embedded convection.

Low-topped convection containing little or no cloud to ground
lightning (such as may occur in cool air masses).

Rapidly evolving convection.

Availability
and Use

The NCWF is available primarily via the Internet from the AWC
Aviation Digital Data Service (ADDS) at https://www.aviationweather.gov/adds/convection/.
Used in conjunction with other weather products such as Convective
SIGMETs, the NCWF provides additional information for convective
weather avoidance and flight planning.

The NCWF access by Automated Flight Service Stations and their
associated En Route Flight Advisory Service facilities, Air Route
Traffic Control Centers (ARTCCs) or Terminal Radar Approach Controls
is planned but NOT currently available.

Display
Summary

Existing convective hazards (based on NEXRAD and lightning data)
are depicted using the color-coded 6-level NCWF hazard scale shown
above. In displaying forecast cell locations, the NCWF does NOT
distinguish among level 3 through level 6.

One-hour forecast locations of signification convection (NCWF
hazard scale levels of 3 or greater) are depicted with blue polygons.
Their directions of movement and storm tops are also shown.

The JavaScript display options include the following (see Figure
7-1-8):

The family of services (FOS) high resolution data service and
server access service.

National
Weather Service Disclaimer

The NCWD/F images displayed on the AWC
web page are all official products of the National Weather Service. On
the bottom of each gif image, there is a short disclaimer, which
describes who should use this product to make scientific decisions
about the state of the atmosphere. The disclaimer reads as follows:
"The NCWF is an automatically generated depiction of: (1) current
convection and (2) extrapolated significant current convection. It is
a supplement to, but does not substitute for, the report and forecast
information contained in Convective SIGMETs."